Motor drive apparatus

Abstract

According to one embodiment, a motor drive apparatus includes a first inverter, a second inverter, and a controller. This controller rotationally moves, at the time of startup of a motor, a rotor of the motor to an initial position by DC excitation of supplying DC exciting currents from the first and second inverters to the phase windings of the motor and, after this rotational movement, PWM-controls switching of the first and second inverters in such a manner that a rotational speed of the rotor becomes a target rotational speed. Then, the controller carries out the DC excitation fey which a zero-axis current in each of the phase windings becomes approximately zero.

What is claimed is: 
     
       1. A motor drive apparatus which drives a motor including a plurality of phase windings arranged in a mutually unconnected state comprising:
 a first inverter which controls electrification to one end of each of the phase windings; 
 a second inverter which controls electrification to the other end of each of the phase windings; and 
 a controller which, at the time of startup of the motor, rotationally moves a rotor of the motor to an initial position by DC excitation of supplying DC exciting currents from the first and second inverters to the phase windings and, after this rotational movement, PWM-controls switching of the first and second inverters in such a manner that a rotational speed of the rotor becomes the target rotational speed, wherein 
 the controller carries out the DC excitation by which a zero-axis current in each of the phase windings becomes approximately zero. 
 
     
     
       2. The motor drive apparatus of  claim 1 , wherein
 DC exciting currents are a plurality of DC exciting currents corresponding to, among combinations of phase currents made to flow through the phase windings by the PWM control, the phase currents of a phase at which the zero-axis currents in each of the phase windings becomes zero. 
 
     
     
       3. The motor drive apparatus of  claim 1 , wherein
 the DC exciting current corresponds to, among combinations of phase currents flowing through the phase windings, phase currents of a phase at which one of phase currents becomes zero and remaining phase currents come to possess values approximately equivalent to each other on the positive side and on the negative side. 
 
     
     
       4. The motor drive apparatus of  claim 3 , wherein
 the phase windings are three phase windings, and 
 the DC exciting currents are three DC exciting currents corresponding to, among combinations of three phase currents made to flow through the phase windings by the PWM control, three phase currents of a phase at which one phase current becomes zero and remaining two phase currents come to possess values approximately equal to each other on the positive side and on the negative side. 
 
     
     
       5. The motor drive apparatus of  claim 1 , wherein
 the phase windings are three phase windings, and 
 the controller controls switching of the first inverter and the second inverter in such a manner that no DC exciting current flows through one phase winding of the three phase windings, a DC exciting current in one direction flows through another phase winding, and a DC exciting current in the other direction flows through a remaining one phase winding. 
 
     
     
       6. The motor drive apparatus of  claim 4 , wherein
 the phase at which the one phase current becomes zero and the remaining two phase currents come to possess values approximately equal to each other on the positive side and on the negative side is 30°, 30°, 150°, 210°, 270° or 330°. 
 
     
     
       7. The motor drive apparatus of  claim 1 , wherein
 the controller 
 rotationally moves, at the time of startup of the motor, the rotor of the motor to the initial position by the DC excitation of supplying DC exciting currents from the first and second inverters to the phase windings, and after this rotational, movement, completes the startup of the motor by rotating the rotor by forced commutation of supplying field-component currents from the first and second inverters to the phase windings, and 
 after the completion of the startup, detects a rotational speed of the rotor on the basis of the phase currents flowing through the phase windings, and PWM-controls switching of the first and second inverters in such a manner that the detected rotational speed becomes the target rotational speed.